Retrospective Cohort Study of Outcomes for Neonates and Infants Undergoing Inguinal Hernia Surgery at Multiple Australian and New Zealand Hospitals: The RetroNeo Study.

Statistical Analysis

1 Introduction

This is the statistical analysis that accompanies the RetroNeo study, which examines the anaesthetic techniques and perioperative outcomes of neonates and infants undergoing inguinal hernia surgery.

2 Results

2.1 Demographics

Characteristic	Overall N = 524 1	Age Categories at Birth
		≤ 27 Weeks N = 49 1	28-32 Weeks N = 116 1	33-36 Weeks N = 123 1	≥36 Weeks N = 236 1
Number of Patients (N)	524	49	116	123	236
Post-Menstrual Age at Birth in Weeks (Median (IQR))	36.1 (31.4, 38.4)	26.0 (24.7, 26.6)	30.1 (28.7, 31.6)	35.3 (34.0, 36.0)	38.7 (38.0, 40.0)
Male Sex (N (%))	440 (84%)	45 (92%)	97 (84%)	105 (85%)	193 (82%)
Weight at Birth in Grams (Median (IQR))	2,140 (1,159, 2,998)	731 (600, 910)	1,203 (935, 1,650)	2,108 (1,800, 2,520)	3,140 (2,600, 3,450)
Location Prior to Day of Surgery
Home/Residential Care	353 (68%)	12 (25%)	60 (52%)	89 (73%)	192 (82%)
Hospital Ward	63 (12%)	4 (8.3%)	12 (10%)	17 (14%)	30 (13%)
NICU	46 (8.9%)	20 (42%)	20 (17%)	4 (3.3%)	2 (0.9%)
PICU	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)
Special Care Nursery	26 (5.0%)	6 (13%)	15 (13%)	5 (4.1%)	0 (0%)
Other Health Care Facility	31 (6.0%)	6 (13%)	9 (7.8%)	7 (5.7%)	9 (3.9%)
Respiratory Support Prior to Surgery
LFNP	37 (76%)	20 (74%)	13 (76%)	3 (75%)	1 (100%)
HFNP	6 (12%)	2 (7.4%)	3 (18%)	1 (25%)	0 (0%)
NIV	1 (2.0%)	0 (0%)	1 (5.9%)	0 (0%)	0 (0%)
ETT	5 (10%)	5 (19%)	0 (0%)	0 (0%)	0 (0%)
NICU Admission Between Birth & Surgery	238 (46%)	48 (98%)	102 (88%)	53 (44%)	35 (15%)
Medical History
Intrauterine Growth Restriction (IUGR)	112 (22%)	15 (31%)	46 (40%)	29 (24%)	22 (9.4%)
Intraventricular Haemorrhage (IVH)	24 (4.6%)	16 (33%)	7 (6.0%)	0 (0%)	1 (0.4%)
Retinopathy of Prematurity	62 (12%)	34 (69%)	27 (23%)	1 (0.8%)	0 (0%)
Congenital Cardiac Disease	56 (11%)	21 (43%)	22 (19%)	7 (5.8%)	6 (2.6%)
Chronic Lung Disease	98 (19%)	44 (90%)	45 (39%)	6 (5.0%)	3 (1.3%)
History of Apnoea (Any Aetiology)	120 (23%)	37 (76%)	65 (56%)	13 (11%)	5 (2.1%)
History of Invasive Ventilation	104 (20%)	40 (82%)	48 (41%)	8 (6.6%)	8 (3.4%)
Respiratory Support at Surgery	49 (9.4%)	27 (55%)	17 (15%)	4 (3.3%)	1 (0.4%)
History of Caffeine Use	122 (23%)	36 (73%)	76 (66%)	10 (8.3%)	0 (0%)
1 n; Median (Q1, Q3); n (%)

2.2 Surgical Details

Characteristic	Overall N = 519 1	Age Categories at Birth
		≤ 27 Weeks N = 48 1	28-32 Weeks N = 116 1	33-36 Weeks N = 122 1	≥36 Weeks N = 233 1
Number of Patients (N)	519	48	116	122	233
Post-Menstrual Age at Birth in Weeks (Median (IQR))	36.1 (31.4, 38.3)	25.9 (24.5, 26.6)	30.1 (28.7, 31.6)	35.3 (34.0, 36.0)	38.7 (38.0, 40.0)
Post-Menstrual Age at Surgery in Weeks (Median (IQR))	44.9 (41.4, 48.1)	41.1 (39.2, 44.1)	41.1 (38.4, 43.5)	44.8 (41.9, 47.9)	47.0 (44.9, 50.1)
Weight at Birth in Grams (Median (IQR))	2,140 (1,150, 2,998)	731 (600, 910)	1,203 (935, 1,650)	2,109 (1,800, 2,540)	3,130 (2,600, 3,450)
Weight at Surgery in Grams (Median (IQR))	4,200 (3,300, 5,205)	3,565 (3,015, 3,990)	3,108 (2,630, 3,700)	3,960 (3,190, 5,115)	4,900 (4,260, 5,600)
Type of Hernia Repair
Bilateral	218 (42%)	31 (65%)	71 (61%)	47 (39%)	69 (30%)
Unilateral	301 (58%)	17 (35%)	45 (39%)	75 (61%)	164 (70%)
Surgical Approach
Laparoscopic	23 (4.4%)	2 (4.2%)	4 (3.4%)	6 (4.9%)	11 (4.7%)
Open	496 (96%)	46 (96%)	112 (97%)	116 (95%)	222 (95%)
Incarcerated Hernia	36 (6.9%)	1 (2.1%)	7 (6.0%)	8 (6.6%)	20 (8.6%)
Additional Associated Procedure	55 (11%)	8 (17%)	12 (10%)	13 (11%)	22 (9.4%)
Total Duration in Minutes (Median (IQR))	74 (59, 94)	97 (74, 122)	79 (61, 103)	73 (59, 88)	70 (56, 85)
Anaesthetic Duration in Minutes (Median (IQR))	71 (55, 91)	93 (70, 115)	74 (57, 100)	69 (53, 85)	69 (54, 83)
Surgical Duration in Minutes (Median (IQR))	34 (25, 47)	50 (36, 67)	37 (28, 53)	32 (22, 43)	31 (25, 44)
1 n; Median (Q1, Q3); n (%)

2.3 Anaesthetic Details

2.3.1 General Anaesthesia

Characteristic	Overall N = 519 1	Age Categories at Birth
		≤ 27 Weeks N = 48 1	28-32 Weeks N = 116 1	33-36 Weeks N = 122 1	≥36 Weeks N = 233 1
Number of Patients (N)	519	48	116	122	233
Anaesthetic Type
GA Only	163 (33%)	13 (28%)	29 (27%)	40 (34%)	81 (36%)
Spinal Only	77 (15%)	7 (15%)	27 (25%)	22 (18%)	21 (9.4%)
Caudal Only	1 (0.2%)	0 (0%)	1 (0.9%)	0 (0%)	0 (0%)
GA + Spinal	4 (0.8%)	0 (0%)	3 (2.8%)	0 (0%)	1 (0.4%)
GA + Caudal	221 (44%)	21 (46%)	40 (37%)	51 (43%)	109 (49%)
GA + Sedation	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)
Spinal + Sedation	8 (1.6%)	2 (4.3%)	2 (1.8%)	1 (0.8%)	3 (1.3%)
Caudal + Sedation	18 (3.6%)	3 (6.5%)	5 (4.6%)	5 (4.2%)	5 (2.2%)
GA + Spinal + Caudal	1 (0.2%)	0 (0%)	1 (0.9%)	0 (0%)	0 (0%)
GA + Caudal + Sedation	5 (1.0%)	0 (0%)	1 (0.9%)	0 (0%)	4 (1.8%)
Type of GA
Sevoflurane	260 (50%)	24 (50%)	49 (42%)	61 (50%)	126 (54%)
Propofol	7 (1.3%)	0 (0%)	2 (1.7%)	3 (2.5%)	2 (0.9%)
Sevoflurane + NO2	46 (8.9%)	4 (8.3%)	11 (9.5%)	9 (7.4%)	22 (9.4%)
Sevoflurane + Propofol	82 (16%)	5 (10%)	12 (10%)	16 (13%)	49 (21%)
Sevoflurane + Dexmedetomidine	6 (1.2%)	0 (0%)	1 (0.9%)	3 (2.5%)	2 (0.9%)
Sevoflurane + Propofol + Dexmedetomidine	4 (0.8%)	1 (2.1%)	2 (1.7%)	1 (0.8%)	0 (0%)
Propofol + NO2	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)
Propofol + Dexmedetomidine	2 (0.4%)	0 (0%)	0 (0%)	0 (0%)	2 (0.9%)
None	112 (22%)	14 (29%)	39 (34%)	29 (24%)	30 (13%)
Type of NMBA
Rocuronium	54 (10%)	12 (25%)	14 (12%)	10 (8.2%)	18 (7.7%)
Vecuronium	58 (11%)	6 (13%)	14 (12%)	11 (9.0%)	27 (12%)
Atracurium	92 (18%)	8 (17%)	18 (16%)	23 (19%)	43 (18%)
Cisatracurium	19 (3.7%)	1 (2.1%)	5 (4.3%)	7 (5.7%)	6 (2.6%)
Suxamethonium	5 (1.0%)	0 (0%)	1 (0.9%)	1 (0.8%)	3 (1.3%)
Suxamethonium + Rocuronium	1 (0.2%)	1 (2.1%)	0 (0%)	0 (0%)	0 (0%)
Suxamethonium + Vecuronium	1 (0.2%)	0 (0%)	0 (0%)	1 (0.8%)	0 (0%)
Suxamethonium + Atracurium	3 (0.6%)	1 (2.1%)	0 (0%)	1 (0.8%)	1 (0.4%)
Suxamethonium + Cisatracurium	1 (0.2%)	0 (0%)	1 (0.9%)	0 (0%)	0 (0%)
None	285 (55%)	19 (40%)	63 (54%)	68 (56%)	135 (58%)
NMBA Reversal Agent
Sugammadex	116 (22%)	6 (13%)	22 (19%)	34 (28%)	54 (23%)
Neostigmine	65 (13%)	10 (21%)	15 (13%)	14 (11%)	26 (11%)
None	338 (65%)	32 (67%)	79 (68%)	74 (61%)	153 (66%)
Paracetramol	219 (42%)	24 (50%)	37 (32%)	54 (44%)	104 (45%)
Parecoxib	7 (1.3%)	0 (0%)	0 (0%)	3 (2.5%)	4 (1.7%)
Opioid	147 (28%)	15 (31%)	22 (19%)	27 (22%)	83 (36%)
Dexmedetomidine	1 (0.2%)	0 (0%)	0 (0%)	0 (0%)	1 (0.4%)
Type of Airway
ETT	339 (65%)	29 (60%)	69 (59%)	82 (67%)	159 (68%)
LMA	49 (9.4%)	2 (4.2%)	5 (4.3%)	8 (6.6%)	34 (15%)
Anaesthetic Face Mask	6 (1.2%)	1 (2.1%)	1 (0.9%)	1 (0.8%)	3 (1.3%)
HFNP	10 (1.9%)	1 (2.1%)	5 (4.3%)	1 (0.8%)	3 (1.3%)
Hudson Mask	3 (0.6%)	0 (0%)	1 (0.9%)	1 (0.8%)	1 (0.4%)
LFNP	19 (3.7%)	8 (17%)	3 (2.6%)	5 (4.1%)	3 (1.3%)
Guedel	3 (0.6%)	0 (0%)	0 (0%)	1 (0.8%)	2 (0.9%)
Chin Support	1 (0.2%)	0 (0%)	0 (0%)	0 (0%)	1 (0.4%)
None	89 (17%)	7 (15%)	32 (28%)	23 (19%)	27 (12%)
1 n; n (%)

2.3.2 Spinal Anaesthesia

Characteristic	Overall N = 90 1	Age Categories at Birth
		≤ 27 Weeks N = 9 1	28-32 Weeks N = 33 1	33-36 Weeks N = 23 1	≥36 Weeks N = 25 1
Number of Patients (N)	90	9	33	23	25
Spinal Local Anaesthetic (Drug (Concentration))
Bupivacaine 0.25%	2 (2.2%)	1 (11%)	1 (3.0%)	0 (0%)	0 (0%)
Bupivacaine 0.5%	39 (43%)	6 (67%)	15 (45%)	10 (43%)	8 (32%)
Levobupivacaine 0.5%	36 (40%)	2 (22%)	11 (33%)	9 (39%)	14 (56%)
Levobupivacaine 0.7%	1 (1.1%)	0 (0%)	1 (3.0%)	0 (0%)	0 (0%)
Ropivacaine 0.2%	1 (1.1%)	0 (0%)	1 (3.0%)	0 (0%)	0 (0%)
None	11 (12%)	0 (0%)	4 (12%)	4 (17%)	3 (12%)
Number of Attempts
1	56 (64%)	6 (67%)	21 (64%)	14 (64%)	15 (63%)
2	20 (23%)	1 (11%)	7 (21%)	5 (23%)	7 (29%)
3	8 (9.1%)	2 (22%)	4 (12%)	1 (4.5%)	1 (4.2%)
4	4 (4.5%)	0 (0%)	1 (3.0%)	2 (9.1%)	1 (4.2%)
Complications
Bleeding	1 (4.2%)	0 (NA%)	0 (0%)	1 (14%)	0 (0%)
Failed Attempt	15 (63%)	0 (NA%)	7 (64%)	3 (43%)	5 (83%)
Inadequate Block	5 (21%)	0 (NA%)	2 (18%)	2 (29%)	1 (17%)
Inadequate Block Duration	2 (8.3%)	0 (NA%)	2 (18%)	0 (0%)	0 (0%)
Inadequate Surgical Conditions	1 (4.2%)	0 (NA%)	0 (0%)	1 (14%)	0 (0%)
Conversion to GA	22 (24%)	1 (11%)	9 (27%)	5 (22%)	7 (28%)
Adjuvant Sedation Used	8 (8.9%)	2 (22%)	2 (6.1%)	1 (4.3%)	3 (12%)
Propofol Sedation	1 (1.1%)	0 (0%)	0 (0%)	1 (4.3%)	0 (0%)
Dexmedetomidine Sedation	1 (1.1%)	1 (11%)	0 (0%)	0 (0%)	0 (0%)
Midazolam Sedation	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)
Clonidine Sedation	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)
Remifentanil	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)
Ketamine Sedation	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)
NO2 Sedation	2 (2.2%)	0 (0%)	2 (6.1%)	0 (0%)	0 (0%)
Sucrose Sedation	4 (4.4%)	1 (11%)	0 (0%)	0 (0%)	3 (12%)
Type of Airway
ETT	1 (1.1%)	0 (0%)	1 (3.0%)	0 (0%)	0 (0%)
LMA	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)
Anaesthetic Face Mask	2 (2.2%)	0 (0%)	1 (3.0%)	0 (0%)	1 (4.0%)
HFNP	2 (2.2%)	0 (0%)	2 (6.1%)	0 (0%)	0 (0%)
Hudson Mask	1 (1.1%)	0 (0%)	0 (0%)	1 (4.3%)	0 (0%)
LFNP	8 (8.9%)	5 (56%)	1 (3.0%)	1 (4.3%)	1 (4.0%)
Guedel	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)
Chin Support	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)
None	76 (84%)	4 (44%)	28 (85%)	21 (91%)	23 (92%)
1 n; n (%)

2.3.3 Caudal Anaesthesia

Characteristic	Overall N = 246 1	Age Categories at Birth
		≤ 27 Weeks N = 24 1	28-32 Weeks N = 48 1	33-36 Weeks N = 56 1	≥36 Weeks N = 118 1
Number of Patients (N)	246	24	48	56	118
Spinal Local Anaesthetic (Drug (Concentration))
Bupivacaine 0.25%	27 (11%)	4 (17%)	6 (13%)	5 (8.9%)	12 (10%)
Bupivacaine 0.5%	1 (0.4%)	0 (0%)	0 (0%)	0 (0%)	1 (0.9%)
Levobupivacaine 0.2%	3 (1.2%)	0 (0%)	1 (2.1%)	1 (1.8%)	1 (0.9%)
Levobupivacaine 0.25%	43 (18%)	3 (13%)	4 (8.5%)	13 (23%)	23 (20%)
Ropivacaine 0.1%	1 (0.4%)	0 (0%)	0 (0%)	0 (0%)	1 (0.9%)
Ropivacaine 0.2%	159 (65%)	16 (67%)	34 (72%)	36 (64%)	73 (63%)
Ropivacaine 0.3%	1 (0.4%)	0 (0%)	1 (2.1%)	0 (0%)	0 (0%)
None	8 (3.3%)	1 (4.2%)	1 (2.1%)	1 (1.8%)	5 (4.3%)
Caudal Additives
Adrenaline	15 (42%)	3 (60%)	2 (40%)	3 (33%)	7 (41%)
Clonidine	18 (50%)	1 (20%)	3 (60%)	5 (56%)	9 (53%)
Dexmedetomidine	1 (2.8%)	1 (20%)	0 (0%)	0 (0%)	0 (0%)
Saline	2 (5.6%)	0 (0%)	0 (0%)	1 (11%)	1 (5.9%)
Number of Attempts
1	191 (79%)	20 (83%)	39 (81%)	39 (71%)	93 (82%)
2	39 (16%)	2 (8.3%)	9 (19%)	12 (22%)	16 (14%)
3	9 (3.7%)	1 (4.2%)	0 (0%)	4 (7.3%)	4 (3.5%)
4	2 (0.8%)	1 (4.2%)	0 (0%)	0 (0%)	1 (0.9%)
Complications
Failed Attempt	10 (100%)	3 (100%)	0 (NA%)	4 (100%)	3 (100%)
Conversion to GA	3 (1.2%)	1 (4.2%)	0 (0%)	1 (1.8%)	1 (0.8%)
Adjuvant Sedation Used	23 (9.3%)	3 (13%)	6 (13%)	5 (8.9%)	9 (7.6%)
Propofol Sedation	15 (6.1%)	2 (8.3%)	4 (8.3%)	3 (5.4%)	6 (5.1%)
Dexmedetomidine Sedation	17 (6.9%)	3 (13%)	5 (10%)	4 (7.1%)	5 (4.2%)
Midazolam Sedation	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)
Clonidine Sedation	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)
Remifentanil	1 (0.4%)	1 (4.2%)	0 (0%)	0 (0%)	0 (0%)
Ketamine Sedation	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)
NO2 Sedation	0 (0%)	0 (0%)	0 (0%)	0 (0%)	0 (0%)
Sucrose Sedation	1 (0.4%)	0 (0%)	0 (0%)	1 (1.8%)	0 (0%)
Type of Airway
ETT	172 (70%)	15 (63%)	37 (77%)	43 (77%)	77 (65%)
LMA	38 (15%)	2 (8.3%)	4 (8.3%)	5 (8.9%)	27 (23%)
Anaesthetic Face Mask	4 (1.6%)	1 (4.2%)	0 (0%)	1 (1.8%)	2 (1.7%)
HFNP	8 (3.3%)	1 (4.2%)	3 (6.3%)	1 (1.8%)	3 (2.5%)
Hudson Mask	2 (0.8%)	0 (0%)	1 (2.1%)	0 (0%)	1 (0.8%)
LFNP	11 (4.5%)	3 (13%)	2 (4.2%)	4 (7.1%)	2 (1.7%)
Guedel	2 (0.8%)	0 (0%)	0 (0%)	1 (1.8%)	1 (0.8%)
Chin Support	1 (0.4%)	0 (0%)	0 (0%)	0 (0%)	1 (0.8%)
None	8 (3.3%)	2 (8.3%)	1 (2.1%)	1 (1.8%)	4 (3.4%)
1 n; n (%)

2.4 Anaesthetic Complications

2.5 Post-Operative Management

2.6 Post-Operative Adverse Events